1. Technical Field
This invention relates to speech communication systems and, more particularly, to systems for digital speech coding.
2. Related Art
One prevalent mode of communication is by communication systems that include both wireline and wireless radio systems. Data and voice transmissions within a wireless system occur within a bandwidth of an allowed frequency range. Due to increased wireless communication traffic, reduced bandwidth of transmissions to improve capacity with the system is desirable.
Voice and data are transmitted digitally in wireless telecommunications due to noise immunity, reliability, compactness of equipment, and the ability to implement sophisticated signal processing functions using digital techniques. One form of digital transmission is accomplished using digital speech processing systems. Waveforms representing analog speech signals are sampled and then digitally encoded. The number of bits of the encoded signal can be expressed as a bit rate that specifies the number of bits to describe one second of speech. Over the years, significant variations and enhancements have been applied to waveform matching techniques in an effort to improve the quality of the synthesized speech and increase the speech compression.
A reduction in the quality of the synthesized (or reconstructed) speech may occur with respect to the original speech. This divergence in the quality of the synthesized speech is due in part to the failure to closely replicate perceptual aspects of the original speech with the bits of data available to describe the signal. Poor replication of the perceptual aspects could result in noise, loss of clarity and the failure to capture recognizable characteristics such as tone, pitch and magnitude. These characteristics allow a listener to recognize who the speaker is, as well as providing other perception based features, such as, intelligibility and naturalness of the speech.
Accordingly, there is a need for systems of speech coding that are capable of minimizing the bandwidth of original speech, while providing synthesized speech that closely resembles the original speech and captures the perceptually important features of the speech.